The present invention relates to a method of determining the severity of a front impact of a motor vehicle, at least one front sensor being installed in the front area of the vehicle to measure a deceleration which is caused by an impact and is used to derive information regarding the severity of the impact.
It is known from British Patent Application 2 293 681 A that one or more front sensors may also be provided in addition to an acceleration sensor situated centrally in the vehicle, their acceleration signals measured in the crash zone in the front area of the vehicle being taken into account in a restraint device (e.g., airbags, seat-belt tightening systems, etc.) deployment decision. With the help of the acceleration measured on impact in the front area of the vehicle, it is possible to obtain information regarding the impact severity. With such information regarding the impact severity, which cannot be obtained with a central acceleration sensor system alone, it is possible to eliminate most cases of faulty deployment and to achieve a very good adaptation of restraint system deployment properties to impact severity. According to the publication cited above, British Patent Application 2 293 681 A, the acceleration measured by the front sensor is integrated, and the integral value is compared with a fixed threshold. If the integral value exceeds this fixed threshold, this means that an impact of a certain severity has occurred. This publication does not indicate how it is possible to differentiate between several different impact severities which differ only slightly.
Therefore, the object of the present invention is to provide a method of the type defined in the preamble with which it is possible to differentiate easily between several different impact severities.
This object is achieved with the features of claim 1 by comparing the deceleration measured by at least one front sensor or the velocity derived from it by integration with a basic threshold which has a characteristic such that it is not exceeded by a measured deceleration/velocity, which is measured in an impact of a severity which does not yet require deployment of restraint devices in the vehicle. At least one additional threshold having a greater slope than that of the basic threshold is formed, this additional threshold having the greater slope branching off from the basic threshold at the point where the basic threshold is exceeded by the measured deceleration/velocity. The slope of the at least one additional threshold is selected so that it is exceeded by the measured deceleration/velocity only at a certain impact severity.
Due to the fact that the deceleration/velocity measured by the front sensor is compared according to the present invention with several thresholds having different slopes, it is possible to differentiate very precisely between various impact severities. Accordingly, the deployment of restraint devices in the vehicle can be adapted to the given impact severity. This adaptation may involve, for example, the rate or degree of inflation of airbags or the choice of airbag inflation levels. A more precise differentiation among various impact severities is also possible since the thresholds are not simply constant values over time but instead have different slopes as a function of time.
Advantageous refinements of the present invention are derived from the subclaims.
It is expedient to provide as many thresholds having different slopes as there are different impact severities to be differentiated.
A very simple means of implementing the thresholds is obtained because of the fact that the basic threshold and each additional threshold begin their chronological course at the beginning of an impact with the same constant minimum value and develop into an individual maximum value having an individual slope after a time lag which is predetermined by the impact severity to be determined.
To allow the use of the least possible computer power in making the threshold value decisions, it is expedient that the individual thresholds develop from a minimum value to their maximum value in a stepped slope characteristic.